1. Field of the Invention
The present invention relates to a control device and a controlled device for remote-controlling a controlled object by using, for example, weak radio waves.
2. Description of the Related Art
A remote control system using weak radio waves has been in wide spread use for door locks of automobiles, automatic doors of parking lots, and the like. If an automobile door lock system is taken as an example, a transmitter (control device) provided in a key holder of a key of the automobile emits radio waves, and a controlled device of the automobile which received the radio waves can unlock the door lock (refer to, for example, JP-A 7-324532 (KOKAI)).
In such a remote control system, there is a need to control only a specific controlled object, so that an exchange of identification signals such as, for instance, IDs has to be carried out. However, if the IDs are simply transmitted, there is a risk that the radio waves are intercepted and the IDs are stolen, and the controlled object is controlled by a third person in an unauthorized manner.
Meanwhile, in the usage of the previously cited door lock of the automobile, there is a need that the transmitter to be operated by a user is made to be small. Further, since the controlled device has to be constantly in an operational state in preparation for the operation from the user, there is a problem that power consumption becomes large. The problem regarding power consumption is particularly important since the control device operated by the user is often driven by batteries. As described above, there is a problem in the conventional control device and controlled device that when the identification signals are intercepted, the controlled object may be controlled in an unauthorized manner. In addition, there is also a problem that the power consumption becomes large while the reduction in size is required.